1. Field of the Invention
The present invention relates to solar power production, and more particularly, to solar receiver panels for use in solar boilers.
2. Description of Related Art
Solar power generation has been considered a viable source to help provide for energy needs in a time of increasing consciousness of the environmental aspects of power production. Solar energy production relies mainly on the ability to collect and convert energy freely available from the sun and can be produced with very little impact on the environment. Solar power can be utilized without creating radioactive waste as in nuclear power production, and without producing pollutant emissions including greenhouse gases as in fossil fuel power production. Solar power production is independent of fluctuating fuel costs and does not consume non-renewable resources.
Solar power generators generally employ fields of controlled mirrors, called heliostats, to gather and concentrate sunlight on a receiver to provide a heat source for power production. A solar receiver typically takes the form of a panel of tubes conveying a working fluid therethrough. Previous solar generators have used working fluids such as molten salt because it has the ability to store energy, allowing power generation when there is no solar radiation. The heated working fluids are typically conveyed to a heat exchanger where they release heat into a second working fluid such as air, water, or steam. Power is generated by driving heated air or steam through a turbine that drives an electrical generator.
More recently, it has been determined that solar production can be increased and simplified by using water/steam as the only working fluid in a receiver that is a boiler. This can eliminate the need for an inefficient heat exchanger between two different working fluids. This development has lead to new challenges in handling the intense solar heat without damage to the system. Typical boilers include two or more sections at different temperatures and pressures, such as a section of steam generator panels, a section of superheater panels, and a section of reheater panels, for example. In a solar boiler, it is advantageous to have boiler sections close together within the receiver where the focused solar radiation provides heat. It has been known, for example, to have one section on top of another section. There is a gap between such adjacent sections, which accommodates headers and associated structures of the boiler sections and can provide room for thermal expansion and contraction of the boiler sections. The gap must be protected against the possibility of focused sunlight reaching components internal to the receiver panels (known as leakage), where the intense radiation can be harmful.
One approach to this problem has been to cover the gaps between boiler sections with a thermal barrier or shield, which blocks the sunlight from entering the gap. Such a thermal barrier occupies surface area in the key receiving area of the boiler and thus reduces the amount of useable solar radiation from the heliostats that is actually received by the boiler.
While the known systems of solar power production have generally been considered satisfactory for their intended purposes, there has remained a need in the art for solar receivers that can improve the useable receiving area while protecting internal spaces from leakage of solar radiation, allowing for thermal contraction and expansion, and providing for drainability. There also has remained a need in the art for such solar receivers that are easy to make and use. The present invention provides a solution to these problems.